Tuning Topology of Dirac and Weyl Semimetals by Pressure

A.K. SoodIndian Institute of Science, Bengaluru

Abstract

Dirac and Weyl semimetals are a new class of topological materials with non-trivial topology in

their bulk electronic structure. The bulk valence and conduction bands cross at discrete points in the

Brillouin zone, called Dirac points, and disperse linearly along all the directions in three

dimensional (3D) momentum space. The Dirac point splits into a pair of opposite chirality Weyl

points if either crystal inversion or time-reversal symmetry is broken as in Weyl semimetals.

My talk will present our recent studies of Dirac semimetal Cd3As2 [1] and Weyl semimetals NbP,

TaP, NbAs and TaAs [2,3] covering Raman spectroscopy, synchrotron x-ray diffraction and

electrical resistivity under pressure using diamond anvil cell and their quantitatively understanding

using first principle density functional theory.

I acknowledge all my collaborators as listed in references below.

[1] Satyendra Nath Gupta, D.V.S. Muthu, C. Shekhar, R. Sankar, C. Felser and A.K. Sood,

Pressure-induced electronic and structural phase transitions in Dirac semimetal Cd3As2: Raman

study; Euro Physics Letter 120, 57003 (2017)

[2] Satyendra Nath Gupta, Anjali Singh, Koushik Pal, D.V.S. Muthu, C. Shekhar, Yanpeng Qi, Pavel

G. Naumov, Sergey A. Medvedev, C. Felser, U.V. Waghmare and A.K. Sood, Pressure-induced

Lifshitz transition in NbP: Raman, x-ray diffraction, electrical transport and density functional

theory; Phys. Rev B 97, 064102 (2018)

[3] Satyendra Nath Gupta, Anjali Singh, Koushik Pal, D.V.S. Muthu, C. Shekhar, Moaz A.

Elghazali, Pavel G. Naumov, Sergey A. Medvedev, C. Felser, U.V. Waghmare and A.K. Sood,

Pressure-induced Lifshitz transition in NbAs: Experiments and Theory; Under Review (2018)

Indo-Italian Synchrotron Collaboration

Andrea LausiHead, Xpress Beamline, Elettra Sincrotrone Trieste

Abstract

Andrea Lausi1, Boby Joseph1, Andrea Goldoni2, Maurizio Polentarutti2, Dipankar Das Sarma3 1Xpress

Beamline, Elettra Sincrotrone Trieste, Trieste, Italy, 2Beamlines Group, Elettra Sincrotrone Trieste, TRIESTE, Italy, 3Solid State and Structural Chemistry Unit, Indian Institute of Science, 560012, Bengaluru, India

Indian research groups have been collaborating with researchers at the Italian Synchrotron radiation source

Elettra since past two decades. The collaboration between Elettra and Indian research institutions is a part of

a wider collaboration between the countries sponsored by the Department of Science and Technology,

Government of India and the Italian Ministry for Foreign Affairs. The high standard of the collaboration in

the field of synchrotron radiation was recognized in the joint statement by the prime ministers of both the

countries, on the occasion of Italian prime minister's visit to India in February 2007. Statistics till 2015

indicate that the collaboration has led few hundred visits of Indian groups to Elettra (with an average of three

scientists per visit) in the last 20 years and to the publication of more than 500 articles in peer-reviewed

scientific journals. Till 2016, Elettra received around 959 experimental proposals from Indian research

groups, corresponding to about 8% of the total: in third place, just after Italy and France (4873 and 1034

proposals respectively). This makes Elettra the most requested European national synchrotron radiation

laboratory by Indian users.

This collaboration has been the earliest possibility for Indian scientists to access synchrotron facilities and

played the most crucial role in building up the synchrotron community within India by making it available to

even those who did not have any prior access or knowledge of synchrotron-based techniques. As a part of

this project, the community was nurtured to become competitive in preparing their proposals that were

evaluated internationally to obtain synchrotron beam-time in various areas of research ranging from solid

state and surface physics to nanotechnology, materials science and life sciences. Great success of these

activities prompted both sides to take a further significant step forward involving the development of two

dedicated beamlines: a macromolecular and a high pressure X-ray diffraction facilities, respectively XRD2

and Xpress, under the partnership between Elettra and Indian Institute of Sciences, Bangalore. Both these

beamlines share a superconducting wiggler as a high flux source. From the beginning of 2016 Xpress

beamline started accepting proposals from external users. This milestone is going play a new chapter in the

scientific collaborations involving Elettra and Indian research community.

Structural Transitions at High Pressures

Goutam Dev MukherjeeIndian Institute of Science Education and Research Kolkata, Mohanpur

AbstractMy journey into the field of study of structural transitions at high pressures started in the XRD1

beamline with the photon flux from bending magnet and now there is a dedicated high pressure

beamline EXPRESS with high brilliance. In this talk I shall first discuss pressure induced structural

behaviour in frame work structured negative thermal expansion material NbOPO4, which shows an

anomaly at 0.6 GPa. Pressure behaviour of unit cell volume changes in linear fashion, and is

followed by a structural amorphization above 20 GPa. This work was published in ELETTRA

Highlights in 2002-2003. Next I shall present our recent work in high pressure XRD studies on

layered WS2 obtained by liquid exfoliation. High pressure X-ray diffraction measurements in

conjunction with Raman studies show the emergence of a triclinic modification along with the

hexagonal phase of WS2 above about 5.8 GPa. However analysis of our ambient and high pressure

studies on monolayer WS2 along with those of the nanocrystalline sample indicate to the presence

of the triclinic phase in patches embedded in the parent hexagonal phase raising a question mark

over the structural purity of the exfoliated monolayered materials beyond a certain stress conditions.

This work has been carried out in EXPRESS beamline.

Structural biology @Elettra: an integrated approach to DNA replication and repair

Silvia OnestiHead, Structural Biology Lab, Elettra Sincrotrone Trieste

AbstractThe Structural Biology Laboratory at Elettra applies molecular and structural biology tools to study

the basic genetic processes within the cell and to characterise some of the proteins involved. We use

protein crystallography to determine the atomic structure of these proteins, as well as biochemical

and biophysical approaches to understand how they work. Crystallographic studies are

complemented by the concomitant use of electron microscopy to visualise the architecture of large

complexes, NMR spectroscopy to study small, disordered regions and small-angle X-ray scattering

(SAXS) to obtain additional structural information. Data from these techniques can be combined

with crystallographic atomic structures to get a three-dimensional picture of the complex

architecture.

Our research focus on DNA replication, recombination and DNA repair. These are crucial events in

the cell cycle, underpinning cellular processes with important consequences such as cell

proliferation and genome stability. Failure to control these processes causes chromosome instability,

which can lead to the development of cellular abnormalities, genetic diseases and the onset of

cancer.

I will present examples derived from our own work aimed at unravelling the structural and

functional aspects of key proteins in these processed, such as the MCM helicase, Cdc45, GINS,

PCNA, and RecQ4. All of these are present in proliferating cells and are highly expressed in

malignant human cancer cells and pre-cancerous cells undergoing malignant transformation.

Therefore, they are ideal diagnostic markers for cancer and possibly targets for anti-cancer drug

development.

http://www.elettra.trieste.it/labs/structural-biology

Structural studies for target characterisation against sepsis causing gram negative bacteria.Ramaswamy S

Institute for Stem Cell Biology and Regenerative Medicine, Bengaluru

AbstractSialic acids (5-N-acetylneuraminic acids, Neu5Ac) are a family of related nine-carbon sugar acids

that are used by bacteria for molecular mimicry, as nutrition, and cell signaling. The motivation for

our program is to understand how bacteria scavenge, transport and incorporate sialic acid into the

lipooligosaccharide (LOS) or lipopolysaccharides (LPS) (Vimr et al, 2004). While some pathogens

have evolved de novo biosynthesis pathways for Neu5Ac many bacteria rely on the acquisition of

Neu5Ac from the environment and hence require high-affinity transport systems. Bacteria

incorporate this scavenged Neu5Ac into the LOS/LPS as the terminal non-reducing sugar. This

sugar is recognized by the complement system in the serum as “self”. Several opportunistic bacteria

use this type of molecular mimicry to evade the immune system, resulting in serious pathological

consequences. It has been shown in H. influenzae that inhibition of the sialic acid transport system

leads to non-virulence in continuous flow biofilm chambers (Allen et al, 2005; Severi et al, 2010).

We propose that the pathway of Sialic acid uptake, catabolism and incorporation would be a very

good drug targets and we should be able to develop anti-microbial agents that act under a variety of

conditions. In order to test this, we have determined structures of proteins involved in scavenging,

transport, catabolism and silica acid incorporation into cell surface glycolipids. I will discuss our

structure-function studies on these proteins from several gram negative bacteria and current efforts

on drug discovery.

The beamlines XAFS and XRF at Elettra:recent highlights and future opportunities

Giuliana AquilantiHead, EXAFS Beamline, Elettra Sincrotrone Trieste

Abstract

The XAFS beamline at Elettra is dedicated to XAS and can operate in a large energy range from 2.4

to 25 keV. The simple optical scheme makes the beamline particularly suitable for transmission

geometry measurements on homogeneous samples for which a large and spatially uniform beam

guarantees high quality data. A fair variety of sample environments and the possibility to practically

adapt any sample environment in the experimental hutch makes the XAFS beamline a quite

appealing instrument as evidenced by the high oversubscription ratio.

The XRF beamline has been conceived to be a multipurpose beamline for x-ray spectrometry and

its endstation hosts an ultra-high vacuum chamber owned by IAEA. This instrument should offer

the possibility to use different x-ray spectrometry techniques such as: x-ray fluorescence, total

reflection x-ray fluorescence, grazing incidence x-ray fluorescence, x-ray reflectometry and x-ray

absorption spectroscopy with submillimetric spatial resolution.

Research highlights for the two beamlines will be shown along with their complementarity. A recent

reorganization of the beamlines’ personnel will allow the user community access to the two

beamlines in a coordinated manner.

Understanding Magneto-structural interactions in Ni-Mn based Heusler alloysK. R. Priolkar

Goa University, Taleigao Plateau, Goa

AbstractNi-Mn based Heusler alloys undergoing austenitic to martensitic transition have been of interest due

to technologically important phenomena like large magnetic field induced strain, large

magnetoresistance, large normal and inverse magnetocaloric effect, etc. These properties are

extremely sensitive to composition of the Heusler alloy as well as the degree of chemical order.

Extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray magnetic circular

dichroism (XMCD) in conjunction with diffraction techniques have been employed to gain an

understanding of atomistic picture of chemical order and effect of composition on martensitic

transition in such Heusler alloys. Systematic investigations on Ni2Mn1+xIn1-x (0 ≤ x ≤ 0.6) reveal

presence of local structural disorder even in the austenitic phase. Despite geometric constraints, Ni-

Mn and Ni-In distances are not equal and the difference between them progressively increases with

increasing Mn content. Presence of chemical disorder results in formation Mn 3d – Ni 3d

hybridized states which are responsible for antiferromagnetic interactions in the martensitic state.

Using Synchrotron to understand properties of doped Nanomaterials: EXAFS and XRD.

Ranjani ViswanathaJawaharlal Nehru Centre for Advanced Scientific Research, Bangalore

AbstractDoping in semiconductor quantum dots as well as nanocrystal heterostructures have been shown to

have distinct advantages for applications. However, diffusion of dopants or impurities in host

nanocrystals out of the host or within the host pose new challenges in determining the nature of

interfaces in heterostructures as well as the interaction environment of the dopant with the host

nanocrystal. While long range phenomena like X-ray diffraction, particularly as a function of

temperature can provide answers to some questions, these long range techniques are not suitable for

analysis such short range phenomena. In this talk, I discuss the use of the use of XRD and EXAFS

to understand properties correlated to doped nanomaterials.

Small angle scattering to investigate the nm-scale: from biology to hard condensed matter

H. AmenitschAustria & Austrian SAXS beamline, Elettra Sincrotrone Trieste

AbstractSmall and Wide Angle Scattering has developed as a standard method to investigate nanostructures

in the range of 0.1 to >100 nm in situ and under in-operando conditions. The enormous benefit of

SAXS compared to many other structural methods is the limited requirements for sample

preparation and environment. This quality enables to study liquids, solids, aerosols and thin films

close the conditions occurring in chemical reactions, temperature treatments and even under more

complicated constrains of in operando investigations such as in supercapacitors or micro chambers

for nanomaterials growth. Therefore, the method allows getting molecular movies on the

nanometer-scale.

This presentation will discuss highlights of the current research program of the Austrian SAXS

beamline covering fields as diverse as structural biology, drug delivery systems or energy materials.

Further, an outlook will be given to the new experimental development as well as emerging

perspectives such as ultra-fast pump probe experiments.

Influence of Confinement on Heme-Protein Function and it’s Consequences on SensingAninda J. Bhattacharyya

Indian Institute of Science, Bengaluru

Abstract

The electroactive centre or site of a biomolecule controls the effective molecular properties at

various length scales. For example, Fe-containing heme proteins, which control storage, transport,

and release of oxygen in most higher forms of life, in biological buffer display a characteristic

quasi-reversible electrochemical behaviour of the FeIIIII couple located in the porphyrin ring.

Encapsulation of these proteins in a variety of hosts (dhost >> dbiomolecule) renders a reversible

electrochemical FeIIIII response. Thus, the reversible redox phenomenon under confinement is

functionally different from that of the protein molecules in the solution. Our objective here is to

understand the fundamental mechanisms behind these changes in the electrochemical response in

the context of protein structure and dynamics under confinement. To develop a comprehensive

mechanistic model, the structure and dynamics of encapsulated proteins are studied using

electrochemical and various techniques including synchrotron and neutron measurements. Control

experiments involving interactions of small molecules, which chemically mimic the protein, with

individual amino acids are also performed. The purpose here is to deconvolute the complex

electrochemical function of heme proteins into simpler interactions. Outcomes of these studies

provided useful inputs on the chemical design of practical electrochemical biosensors.

In-situ SAXS and Diffraction Studies of Nanostructure-Self-Assembly ProcessesMilan K. Sanyal

Saha Institute of Nuclear Physics, Kolkata

AbstractFormation of ordered structures with nanoparticles is an evolving field of research as control over

this self assembly process is essential to develop cost-effective nanostructures in robust engineering

form and to investigate predictions of low dimensional physics. Physical/chemical properties of

nanoparticles, ranging from chemically-formed novel materials to physically deposited quantum

dots grown in extremely controlled environment, can be tuned by altering shape, size and

compositions. However understanding structural features of individual nano-sized materials and

assembly of these particles is a nontrivial exercise. Availability of intense photon sources in

synchrotrons is giving us the opportunity to investigate in-situ individual nanoparticles and the self-

assembly processes with small angle x-ray scattering (SAXS) and x-ray diffraction techniques. We

shall illustrate this topic with few of our recent results.

References:

1. In-Situ GISAXS Study of Supramolecular Nanofibers having Ultrafast Humidity Sensitivity,

A. Bhattacharyya, M. K. Sanyal, U. Mogera, S. J.George, M. K. Mukhopadhyay, S. Maiti

and G.U. Kulkarni, Scientific Reports 7, 246 (2017).

2. Evidence of contact epitaxy in the self-assembly of HgSe nanocrystals formed at a liquid–

liquid interface, S. Maiti, M. K. Sanyal, M. K. Jana, B. Runge, B. M. Murphy, K. Biswas

and C. N. R. Rao,

J. Phys.: Condens. Matter 29, 095101 (2017).

Synchrotron Radiation and Cultural Heritage:The Experience of Elettra

Franco ZaniniHead, SYRMEP-Imaging Beamline, Elettra Sincrotrone Trieste

Abstract

The use of synchrotron radiation for the analysis of samples of historical and artistic importance has

been increasing over the past years, and experiments related to the study of our cultural heritage

(CH) have been routinely performed at many beamlines of Elettra, the Italian synchrotron radiation

facility. The laboratory now offers a platform dedicated to CH researchers in order to support both

the proposal application phase and the different steps of the experiment, from sample preparation to

data analysis.

TwinMic, the European Soft X-ray Transmission and Emission Microscope, integrates the

advantages of complementary scanning and full-field imaging modes into a single instrument.

TwinMic operates in the 400-2200 eV energy range. This microscope station has been designed as

highly modular in its optical configuration and specimen environment, and an international

community of scientists and technicians continuously improves the instruments performance and

versatility to suit the experimenter's requirements.

X-Ray Fluorescence is a highly versatile beamline working in an energy range between 2 and 14

keV. The beamline is optically designed to present beam parameters needed for high level

measurements in spectroscopy as well as in microscopy. The beamline hosts an ultra-high vacuum

chamber, in partnership with the IAEA, which will allows the synergistic application of various X-

Ray Fluorescence techniques together with X-ray Absorption Near Edge Structure (XANES) and X-

Ray Reflectometry.

The flexible design of the MCX beamline allows a wide range of non-single crystal diffraction

experiments relevant for the cultural heritage, from phase identification to atomic structural studies.

Other powder diffraction techniques that can be applied to cultural heritage materials comprise

texture and orientation determination of the crystalline phases and the determination of the

microstructure of the sample in terms of crystallite size, defects characterization and accumulated

strain.

SYRMEP, the X-ray microimaging and microtomography station, with an energy range of 8.3 - 35

keV, is a highly flexible beamline allowing the analysis of samples in both absorption and phase

contrast mode. The versatility of this instrument has attracted researchers from different

communities, from restoration and conservation to art history, archaeology and paleoanthropology.

The XAFS beamline, working in the energy range between 2.4 and 27 keV, provides microscopic

structural information through the analysis of a sample X-ray absorption spectrum, with unique

applications in the field of cultural heritage. It is a powerful local structural probe, which does not

require long-range order, and allows the determination of the chemical environment of a single

element in terms of number and type of neighbours, interatomic distances and structural disorder.

UV resonant Raman spectroscopy performed at IUVS beamline has been demonstrated to be a non-

destructive powerful tool for obtaining a detailed compositional characterization of pigments

present in artworks of historical-artistic interest. Thanks to the exploiting of the resonant conditions

occurring for specific functional groups at different excitation wavelengths in the UV-range and the

strong reduction of the interfering fluorescence background that often seriously limits the use of

conventional Raman spectroscopy in cultural heritage studies, UV resonant Raman scattering

constitutes an alternative spectroscopic approach for achieving a non-destructive identification of

the main pigmenting agents.

Infrared Microscopy techniques at SISSI beamline offer the possibility to correlate the sample

morphological features with its vibrational local pattern at diffraction limited spatial resolution.

Chemical information on both organic and inorganic constituents of art pieces can be obtained at

SISSI, exploiting several sampling methodologies, suitable for probing thin sections and material

surface properties as well.

The Scanning photoelectron microscope (SPEM) hosted at the ESCA microscopy beamline allows

to combine chemically surface sensitive measurements with high spatial resolution. A beam spot

down to 120 nm and energy sensitivity within 180 meV using a third generation X-ray source

providing more than 109 photons/s in the probe has opened the opportunity for CH to perform

surface micro-characterization. The experimental apparatus allows to carry out a manifold of

experiments, aiming at quantitative and qualitative chemical characterisation of morphologically

complex materials.

Evolution of Structures at the Air-Water Interface

Alokmay DattaSaha Institute of Nuclear Physics, kolkata

Abstract

The air-water interface is itself a dynamic structure with a hierarchy of timescales. This is related to

the coexistence of interchanging hydrogen-bonded structures of water which give rise to a slightly

negatively charged surface with an unusually high free energy. Introduction of charged or polar

bodies to this interface sets up new dynamics that lead to correlated structures ranging from sub-

nanometer to several hundred micrometers and even beyond.

These structures can be transferred onto suitable substrates and probed. Understanding the role of

molecular bonding on these structures possibly holds the key to control and functionalise them.

Ultraviolet and Soft X-ray spectroscopy is an invaluable tool to probe the bonding and correlating

this information with structural and morphological data. In this talk I shall present the results on

structures evolving under ion-molecule and nanoparticle-molecule forces.

Biophysics and Nanomedicine at the Elettra NanoInnovation LabLoredana Casalis

NanoInnovation Lab, Elettra Sincrotrone Trieste

Abstract

The NanoInnovation Lab of Elettra works on applications of nanotechnologies to biophysics and

translational medicine. The focus is mainly on world spread diseases, as cancer and

neurodegenerative diseases. We implement innovative sensing strategies for the detection of disease

molecular biomarkers at the early stage of disease progression, as well as integrated platforms to

decipher the mechanisms of diseases development. Our platforms are based on Atomic Force

Microscopy (AFM), to study biorecognition events as well as cell and tissue biomechanics, and are

complemented by Fluorescence Microscopy, Electrochemical Impedance Spectroscopy and other

Synchrotron Radiation-based techniques.

Spectroscopy of self-assembled networks and nano systems

Dinesh TopwalInstitute of Physics, Bhubaneswar

Abstract

Abstract: The confinement effects of electrons in ultra-thin films and nanowires grown on metallic

and semiconducting substrates will be discussed. Finite electron reflectivity at the interface is

sufficient to sustain the formation of quantum well states and weak quantum well resonance states

even in closely matched metals. The expected parabolic dispersion of sp derived quantum well

states for free standing layers undergoes deviations from parabolic behaviour and undergoes

modifications due to the underlying substrate bands, suggesting the effects of strong hybridization

between the quantum well states and the substrate bands. I will also discuss electronic structure of

ordered Ag-Bi alloy and their surface-state (SS) bands, spin split by the Rashba interaction,

selectively coupled to the quantum-well state (QWS) bands, originally spin degenerate, in the metal

film.

XRD2 - the new indo-italian beamline for macromolecular crystallographyMaurizio Polentarutti

XRD1 Beamline, Elettra Sincrotrone TriesteAbstract

The new beamline XRD2 at the Elettra synchrotron, dedicated to macromolecular cryustallography,is ending the commissioning phase. The XRD2 project is developed in partnership with the Indianscientific community and administered through Elettra and Indian Institute of Science (IISc),Bengaluru.

A new beamline has been constructed at section 11.2 at the Elettra synchrotron and is nowcompleting the commissioning phase. The high photon flux provided by the SuperConducting multipole Wiggler (SCW), installed at the 11.2 section, permits the operation of threebeamlines, a central tunable and two fixed energy beamlines.

The XRD2 beamline will be complementary to the existing general-purpose XRD1. XRD2beamline will be dedicated to high throughput macromolecular crystallography experiments: largetunable energy range (8.0 - 35.0 keV) for SAD/MAD experiments, automated sample mounting in acryogenic environment and high speed large area detector are some of the important features ofthis beamline.

Beamline features (energy resolution, flux, spot dimensions) as well as sample changer capabilitieswill be reported together with data quality indicators from data collected on standard-test (lysozyme) and real-life samples.

Crystal structure determination of nucleotide-dependent restriction-modification enzymes

SaikrishnanIndian Institute of Science Education and Research, Pune

Abstract

Nucleoside triphosphate-dependent restriction-modification enzymes are the most prominent

bacterial defence against foreign DNA invasion. The enzymes have a nucleotide-dependent

endonuclease activity that cleaves foreign DNA that enters the host cell. Molecular details of the

activities of these enzymes have remained unravelled due to lack of structural information in atomic

detail. Efforts to obtain the structural data has been hindered by the large size and complex nature of

these enzymes. My laboratory has over the years been carrying out structural studies on these

enzymes primarily using X-ray crystallography. These studies have led to the first snapshots of the

enzymes in action. I will discuss the ways and means employed by us towards obtaining these

snapshots, and also the mechanistic details that have emerged from these studies.

Applications of synchrotron radiation for integral membrane protein structures.Aravind Penmatsa

National Centre for Biological Sciences, Bengaluru

AbstractSynchrotron radiation from insertion devices is highly successful at getting high resolution data

from crystals of membrane proteins which tend to have high levels of solvent content and/or are

very small in size. Using the case study of the dopamine transporter, I will put forth the immense

potential of obtaining high resolution structural information for membrane proteins, that are not

very easy to crystallize. Integral membrane proteins are also crystallized in lipidic cubic phase that

allows formation of type-I crystals. Cubic phase crystals tend to be micron sized and are prone to

radiation damage. Attempts to crystallize the dopamine transporter in complex with an antibody

yielded cubic phase crystals from which a dataset could be stitched together using data from seven

crystals. My talk will focus on the extensive modification done to the protein, crystallization trials

and the use of synchrotron radiation that helped reveal the structure of the dopamine transporter.

Molecular Orbital Tomography: adsorption geometry and electronic structure

V. FeyerHead, NanoESCA Beamline, Elettra Sincrotrone Trieste

Abstract

Angle-resolved photoelectron spectroscopy (ARPES) is a well-established method to study the band

structure of and recently it has been shown that it can also provide an alternative route to obtain

information regarding the charge distribution of individual molecular orbitals [1, 2]. Under specific

assumptions about the final state of the photoemitted electron, molecular orbital structures can be

investigated using data from the angle-resolved photoemission. This approach, based on the

comparison between ARPES measurements and theoretical calculations, forms the basis of

molecular orbital tomography (MOT).

The photoemission current (I) within the dipole approximation is proportional to:

where and are the polar and azimuthal emission angles, respectively. I is given by the sum over

all transitions from the occupied initial states i to the final states f characterized by the direction

( ) and the kinetic energy of the photoemitted electron. The final state, in the most simple

approach, can be approximated by a plane wave (PW) only characterized by the direction and wave

number of the emitted electron [1] :

For organic molecules, the photocurrent of a well-defined initial state can be selectively measured,

when the energetic separation of individual molecular orbitals is bigger than the intermolecular

band dispersion. This allows the measurement of |i(k)| and, via a subsequent inverse Fourier

transform, the reconstruction of molecular orbital densities in real space, providing a new tool for

the investigation of organic molecular films on metallic substrates.

As example, in the talk I will show the investigation of the adsorption behavior of nickel

tetraphenyl porphyrin (NiTPP) molecules on the Cu(100) surface by applying a comprehensive

multi-technique approach, photoemission electron microscopy (PEEM), MOT and scanning

tunneling microscopy (STM), complemented density functional theory (DFT) calculations [3]. The

adsorbed NiTPP arrange in two different geometrical configurations with different orientation

respect to [100] crystal direction. By combining STM with DFT calculations, we demonstrate that

the contrast, in STM images, arises mainly from the phenyl peripheral groups, which are tilted

upwards. This adsorption configuration prevents the macrocycle, where frontier orbitals are

localized, to be resolved by the STM tip. For this reason, STM cannot be used for mapping the

charge distribution of the highest occupied and lowest unoccupied molecular orbitals (HOMO and

LUMO, respectively). Therefore, as a complementary technique, we exploited the capability of our

PEEM to directly image a wide reciprocal space in one single shoot. The ARPES data were then

compared to DFT calculations, within the MOT framework. The molecular orbitals exhibit peculiar

features which can be used to unambiguously identify them in the valence band spectra. This is

particularly useful to determine the molecule-substrate interaction and the charge transfer

phenomena between adsorbed molecules and metal surfaces. The comparison between experiment

and theory shows that the former gas-phase LUMO+3 becomes occupied upon adsorption on the

metal surface. This unexpected result suggests that a multi-technique approach is mandatory in

order to obtain a consistent picture of the adsorption behavior and electronic properties of the

molecular system.

[1] Puschnig, P. et al. Science 326, 702–706 (2009).

[2] Ziroff, J., et al. Physical Review Letters 104, 233004.

[3] Zamborlini, G. et al. Nature Communicationsvolume 8, Article number: 335 (2017)

Infrared Spectroscopy using Synchrotron RadiationHimali Bhatt

Bhabha Atomic Research Centre, Trombay, Mumbai

AbstractInfrared spectroscopy, in particular, IR microspectroscopy, has matured from a simple analytical

technique to a rigorous micro-structural technique, owing primarily to the advent of Fourier

Transform interferometry and synchrotron radiation as the illuminating source, among other factors.

It is the brightness advantage of the synchrotron radiation, the directed emission from relativistic

electrons in the storage ring, which leads to the focussing capabilities of the long wavelength IR

light to a spot size comparable with the diffraction limit. This results in a specific advantage of

enhanced signal to noise ratio from microscopic specimens, thus benefitting the fields of high

pressure physics, IR imaging of tiny biological samples like tissues, hair cross sections etc., optical

properties of single crystals and surface science. In this talk, the design and capabilities of

synchrotron IR beamlines, BL-6 at the Indian synchrotron radiation source, Indus-1 and the Italian

SISSI beamline at Elettra synchrotron radiation source will be discussed and compared. Typical

case studies on synchrotron high pressure infrared studies of proton dynamics in strong hydrogen

bonds of molecular solids and pressure effects on the superconducting materials will be presented.

In addition, the use of in-situ low temperature technique for deducing vibrational structure and

optical properties will also presented, highlighting the crucial micro-structural information extracted

using infrared spectroscopy of materials under extreme thermodynamic environments. The

information, thus obtained, can be used with the complementary techniques using x-ray and neutron

sources, for extracting comprehensive structural details of the samples.

Superconductivity in Ferro-pnictides

Kalobaran MaitiTata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai

Abstract

Superconductivity in Fe-based compounds is believed to appear due to spin fluctuations. Recent

studies, however, revealed mysterious superconductivity with high transition temperature under

pressure and/or chemical substitution, where the compound do not show magnetic order. There are

controversies on the relation between hydrostaticity of the pressure and superconductivity. We

studied the Fermiology of some of the 122 class of compounds employing angle resolved

photoemission spectroscopy (ARPES). The Fermi surfaces at different temperatures reveal

importance of strain induced effects in the electronic structure. We show that the evolution of FS

topology in CaFe2As2 is not directly driven by the structural transition. In addition, we discover the

existence in ambient conditions of energy bands related to the collapsed tetragonal phase. These

bands are distinctly resolved in the high-photon energy spectra exhibiting strong Fe 3d character.

They gradually move to higher binding energies due to thermal compression with cooling, leading

to the emergence of 3D topology in the Fermi surface. The results of EuFe2As2 exhibit signature of

coherent polaron at low temperatures. Our time resolved ARPES results show orbital selective

behavior in EuFe2As2.These results reveal the existence of hidden parameters, which are argued to

lead to quantum fluctuations responsible for the exotic electronic properties in Ferro pnictide

superconductors.

References:

[1] Khadiza Ali, Swapnil Patil, Ganesh Adhikary, Sangeeta Thakur, S. K. Mahatha, A. Thamizhavel, G.

De Ninno, Paolo Moras, Polina M. Sheverdyaeva, C. Carbone, L. Petaccia and Kalobaran Maiti,

Phys. Rev. B 97, 054505 (2018). [2] Khadiza Ali and Kalobaran Maiti, Scientific Reports 7, 6298 (2017).[3] G. Adhikary, B. Ressel, M. Stupar, P. R. Ribič, J. Urbančič, G. De Ninno, D. Krizmancic, A.

Thamizhavel, and Kalobaran Maiti, arXiv:1711.05464v2.[4] G. Adhikary et al., J. Appl. Phys. 115, 123901 (2014).[5] G. Adhikary et al., J. Phys.: Condens. Matter 25, 225701 (2013).[6] G. Adhikary et al., J. Appl. Phys. 114, 163906 (2013).

A low-photon-energy ARPES system for band mapping and many-body effects in solid materials

Luca PetacciaBaDElph Beamline, Elettra Sincrotrone Trieste

AbstractThe BaDElPh beamline is an undulator-based normal incidence monochromator

(NIM) instrument which provides photons in the energy range 4.6-40 eV with

high flux, high energy resolution, and horizontal-vertical linear polarization [1].

The beamline serves an end station to perform primarily high-resolution angle-

resolved photoemission spectroscopy (ARPES) experiments from solids in the

low photon energy regime. Photon energies lower than 15 eV provide enhanced

bulk sensitivity, allow for the highest momentum and energy resolution, and

are useful for tuning matrix elements which vary rapidly at low energy. The

availability of such low photon energies for high-resolution ARPES studies

makes BaDElPh unique at Elettra and it is one of the few beamlines available

worldwide. In this talk, the status and performance of the system will be

presented with also a review of some recent scientific results.

[1] www.elettra.eu/elettra-beamlines/badelph.html

Atomic, molecular and cluster physics with novel XUV light sources

Dr. M. Coreno ISM-CNR and Elettra Sincrotrone Trieste

Abstract

XUV facilities at third generation synchrotron laboratory, like the Gas Phase Photoemission

beamline of the Elettra storage ring (Trieste, Italy) have enabled thorough photoionization studies of

isolated systems for more than 20 years [1]. More recently, the interest of the atomic and molecular

physics community has been attracted by the opportunity of exploring the temporal dynamics of

isolated systems by means of novel state-of-the-art light sources. Thus, our group has taken active

part in the development of two novel XUV facilities: the Low Density Matter (LDM) beamline [2]

at the FERMI free electron laser [3], and CITIUS [4], a state-of-the-art fs-VUV source, based on

laser High Harmonic Generation on rare gases. Recent experiments on photoionization

spectroscopy of gas phase molecular targets of increasing complexity will be presented, as well as

research opportunities opened in the field of atomic, molecular and cluster physics by these novel

ultrafast light sources.

Keywords: Photoionization Spectroscopy; Photoelectron Spectroscopy; Synchrotron Radiation

References

[1] K.C. Prince, et al J. Synch. Rad. 5 (1998) 565;

see also at http://www.elettra.eu/elettra-beamlines/gasphase.html

[2] V. Lyamayev, et al. J. Phys. B 46 (2013) 164007. See also

http://www.elettra.eu/lightsources/fermi/fermi-beamlines/ldm/ldmhome-page.html

[3] “Free Electron laser Radiation for Multidisciplinary Investigations” . See e.g.

E. Allaria, et al. New J. Phys. 14 (2012) 113009.

[4] C. Grazioli, et al. , Rev. Sci. Instr. 85 (2014) 23104. See also

https://www.elettra.eu/lightsources/labs-and-services/citius/citius.html

Unravelling the photodynamics of mesoscopic aggregates hosted on quantum fluid clusters:from synchrotrons towards free-electron lasers

Sivarama KrishnanIndian Institute of Technology, Madras

AbstractAdvanced modern light sources, especially the third generation, to which the Elettra synchrotron

belongs, offer unique opportunities to probe quantum systems. When combined with powerful

coincidence spectroscopy techniques we can find answers to generic questions as well as specific

details of the photodynamics of two- and, indeed, multi-component systems. In particular, we have

probed in a series of experiments over the last five years aggregate mesoscopic systems formed in

or on quantum fluid clusters, superfluid He nanodroplets [1]. Beginning with the first

photoelectron-photoion coincidence (PEPICO) spectroscopy on these systems enabled by the

workstations at Elettra, we will present key results and finding [2, 3].

Current and future directions in investigating the photodynamics of these systems is focussing on

multi-electron processes in these complex systems where classic Fano profiles [4] have been

observed and studied, inter-atomic Coulomb decay and electron transfer mediated decay [5] has

been evidenced and even multiple ionization following Penning and excitation transfer has been

found to occur [6].

We will present both published results as well as findings from ongoing work. These pave way and

motivate further experiments involving free electron lasers where the dynamics and timescales of

these processes can be probe directly and unambiguously.

References:[1] J. P. Toennies et al., Annual review of physical chemistry 49.1, 1-41 ((1998)[2] D Buchta et al., The Journal of chemical physics 139 (8), 084301 (2013)[3] D Buchta et al., The Journal of Physical Chemistry A 117 (21), 4394-4403 (2013)[4] A C LaForge et al., Physical Review A 93 (5), 050502 (2016)[5] A C LaForge et al., Physical review letters 116 (20), 203001 (2016) [6] S. R. Krishnan et al., (manuscript under review).

High Pressure studies to unravel exotic states of matter

Chandrabhas NarayanaJawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru

Abstract

The talk will be providing an introduction to the area of high pressure in condense matter with

examples which brought out exotic understanding of science of materials. Specifically, how

pressure is a very excellent tool for perturb a system and studying exotic phase of the materials. As

an example, Ice like phase of NH4F will be shown to suggest how tetrahedrallly coordinated system

with different bonding can mimic the rich Ice phase diagram. At the end, we will be providing the

latest result of high pressure results on TiTe2 studied at ELETTRA which shows topological phases

under pressure.

MCX: More than just powdersJasper Plaisier

Head, MCX-Powder Diffraction Beamline, Elettra Sincrotrone Trieste

AbstractThe beamline MCX is the powder diffraction beamline of Elettra – Sincrotrone Trieste. The

beamline can host all routine applications of powder diffraction, such as phase identification and

quantification, structure determination, grazing incidence diffraction on thin films and line profile

analysis. However, the possibilities offered by MCX don’t stop there. The experimental station is

designed in such a way, that it is possible to perform measurements on a large variety of samples,

such as batteries, mechanical parts or objects of cultural heritage. The availability of various

detectors (0D, 2D and silicon drift) opens up a world of experiments, that can be performed at

MCX. In this presentation the capabilities of the beamline are illustrated by e series of examples of

experiments that have recently been conducted focusing on non-standard diffraction measurements.

The examples include stress measurements on alloys treated by laser peening, high temperature

experments under controlled atmospheres and operando battery measurements.

Investigation of polymorphism under pressure using synchrotron x-ray diffractionH. K. Poswal

High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai

AbstractPhysical state of a material is uniquely defined by the thermodynamic conditions (i.e., pressure and

temperature) it is subjected to. At particular state of material, the physical properties are governed

by the inter-atomic or intermolecular bondings, which in turn depend primarily on the electronic

structure. These electronic states, arising from the overlap of the electronic wave functions, can be

significantly altered by the pressure and temperature, as these affect the inter-atomic distances.

These distances can be substantially altered during structural transition. The advancement in the

development of diamond anvil cell (DAC) and synchrotron radiation sources made it possible to

investigate the materials under extreme high pressure conditions. The structural response of

materials to high pressures can be investigated using bright synchrotron x-ray sources. In this

presentation, pressure induced polymorphism in the materials will be discussed through a few

representative studies carried out at ECXRD beamline Indus-2 and Elettra synchrotron radiation

sources.